7 장 Transmission media( 전송매체 )

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7 장 Transmission media( 전송매체 )

7.1 Guided Media( 유도매체 )

7.2 Unguided media( 비유도매체 )

7.3 Performance( 성능 )

7.4 요약

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전송매체 (cont’d)

~ Can be divided into two broad categories :

유도매체 , 비유도매체

Classes of transmission media

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7.1 Guided Media( 유도매체 )

Categories of guided media

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유도매체 (cont’d)Twisted-Pair Cable

~ comes in two forms : unshielded( 비 차 폐 ) and shielded( 차폐 )

UTP(Unshielded Twisted-Pair) Cable~ is the most common type of telecommunication

medium in use today.

Frequency range for twisted-pair cable

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유도매체 (cont’d)

Twisted-Pair Cable~ consists of two conductors (usually copper), each

with its own colored plastic insulation.

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Effect of noise on parallel lines

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Effect of noise on twisted-pair lines

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유도매체 (cont’d)Advantage of UTP

~ is cheap, flexible, and easy to install.

Cable with 5 unshielded twisted pairs of wires

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유도매체 (cont’d)UTP standards has developed to grade by quality

Category 1 : basic twisted-pair cabling (telephone systems)

Category 2 : suitable for voice and for digital data transmission of up to 4 Mbps

Category 3 : ~ used for data transmission of up to 10 Mbps(now standard cable)

Category 4 : possible transmission rate to 16Mbps Category 5 : ~ used for data transmission up to 100Mbps

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유도매체 (cont’d)UTP connectors

~ a type of snap-in plus like that used with telephone jacks.

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STP(Shielded Twisted-Pair) cable~ has the same quality consideration as UTP (more

expensive, less susceptible to noise)

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동축 케이블 (Coaxial Cable)~ carries signals of higher frequency ranges

Frequency range of coaxial cable

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Coaxial cable

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Coaxial Cable Standards

~ are categorized by RG(radio government)

RG-8 (used in Thick Ethernet)



RG-58 (used in Thin Ethernet)

RG-75 (used for TV)

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Optical Fiber( 광섬유 )~ is made of glass or plastic and transmits signals in

the form of light

Nature of Light~ is a form of electromagnetic energy. It travels at its

fastest in a vacuum : 300,000km/s. This speed decreases as the medium through which the light travels become denser.

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굴절 (Refraction)

* Fiber-optic technology takes advantage of the properties shown in Figure 7.13b to control the propagation of light through the fiber channel.

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임계각 (critical angle) As the angle of incidence( 입사각 ) increase, it

moves away from vertical and closer to the horizontal.

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반사 (Reflection) When the angle of incidence becomes greater than

the critical angle, a new phenomenon occurs called reflection

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유도매체 (cont’d)Propagation Model

current technology supports two models for propagating light along optical channel.

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Multimode~ multiple beams from a light source move through

the core in different paths.

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Multimode graded-index

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Single Mode~ uses step-index fiber and a highly focused source

of light that limits beams to a small range of angles, all close to the horizontal.

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Fiber sizes~ are defined by the ratio of the diameter of their

core to the diameter of their cladding.

Fiber Type Core(microns) Cladding(microns)

62.5/125

50/125

100/140

8.3/125

62.5

50

100

8.3

125

125

140

125

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유도매체 (cont’d)Cable Composition

Fiber can be made of either glass or plastic Inner core must be ultrapure and completely regul

ar in size and shape Outer jacket can be made Teflon coating, plastic c

oating, fibrous plastic, metal tubing, and metal mesh

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Light Sources for optical label LED(Light-Emitting Diode) : Short distance ILD(Injection Laser Diode) : Long distance

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Fiber-Optic Connectors~ must be as precise as the cable itself.

~ All of the popular connector are barrel( 원 통 ) shaped and come in male and female versions.

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Advantages of Optical Fiber Noise resistance Less signal attenuation Higher bandwidth

Disadvantages of Optical Fiber Cost Installation/maintenance Fragility

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7.2 비유도 매체 (Unguided media)

wirelesssignals are broadcast through air

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비유도 매체 (cont’d)

Radio Frequency Allocation

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Propagation of radio waves Types of propagation

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Type of propagationSurface Propagation

~ Radio wave travel trough the lowest portion of the atmosphere( 대기권 )

Troposphere( 대류권 ) Propagation~ can work two ways( signal can be directed in a straight

line from antenna to antenna. It can be broadcast at an angle into the upper layers of troposphere where it is reflected back down to the earth’s surface

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Ionosphere( 전리층 ) Propagation~ High-frequency radio waves radiate upward into the io

nosphere where they are reflected back to earth

Line-of-Sight Propagation~ Very high frequency signals are transmitted in straight

lives directly from antenna to antenna

Space Propagation~ utilizes satellite relays in place of atmospheric retractio

n

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Propagation of Specific Signals~ The type of propagation used in radio transmission

depends on the frequency(speed) of the signal

VLF(Very Low Frequency)~ are propagated as surface waves, usually through

air but sometimes through seawater

~ are used mostly for long-range radio navigation and for submarine communication

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LF(Low Frequency)~ are also propagated as surface waves

~ are used for long-range radio navigation and for radio beacons or navigation locators

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MF(Middle Frequency) are propagated in the troposphere( 대류권 ) are absorbed by the ionosphere uses for MF transmissions include AM radio,

maritime radio, radio direction finding(RDF), and emergency frequencies

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비유도 매체 (cont’d)HF(High-Frequency)

~ use ionospheric propagation

~ uses of for HF signals include amateur radio(ham radio), CB(Citizen’s band) radio, international broadcasting, military communication, long-distance aircraft and ship communication, telephone, telegraph, and facsimile

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VHF(Most Very High Frequency)~ use line-of-sight propagation

~ uses for VHF include VHF television, FM radio, aircraft AM radio, and aircraft navigational aid

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비유도 매체 (cont’d)UHF(UltraHigh Frequency)

~ always use line-of-sight propagation.

~ uses for UHF include UHF television, mobile telephone, cellular radio, paging , and micro wave links

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SHF(SuperHigh Frequency)~ are transmitted using mostly line-of-sight and som

e space propagation.

~ uses for SHF include terrestrial and satellite microwave, and radar communication

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EHF(Externally High Frequency)~ use space propagation

~ uses for EHF are radar, Satellite, and experimental communication

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Terrestrial microwave~ require line-of-sight transmission and reception eq

uipment. The distance coverable by a line-of-sight signal depends to a large extent on the height of the antenna : the taller the antenna, the longer the sight distance

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비유도 매체 (cont’d)Repeaters

~ To increase the distance served by terrestrial microwave, a system of repeaters can be installed with each antenna.

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Antennas~ two types of antenna

Parabolic dish~ is based on the geometry of a parabola

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Horn antenna~ looks like a gigantic scoop

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비유도 매체 (cont’d)Satellite Communication

~ is much like line of sight microwave transmission in which one of the station is a satellite orbiting the earth

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Geosynchronous satellites

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Frequency bands for satellite communication

`

Band Downlink Uplink

C

Ku

Ka

03.7 - 04.2 GHz

11.7 - 12.2 GHz

17.7 - 21.0 GHz

05.925 - 06.425 GHz

14.000 - 14.500 GHz

27.500 - 31.000 GHz

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Cellular telephony~ is designed to provide stable communications

connections between two moving device or between one mobile unit and one stationary(land) unit.

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Cellular System

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Cellular Bands Tradition cellular transmission is analog. The FCC has assigned two bands for cellular use.

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비유도 매체 (cont’d)Transmitting

The caller enter a code of 7 or 10 digits(phone number)

Press the send button

The mobile phone then scans the band, seeking a setup

channel with a strong signal

Sends the data(phone number) to the closest cell office

Cell office relays the data to the MOS0

MTS0 send data on to the telephone central office

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비유도 매체 (cont’d)Receiving

Telephone central office sends the number to the MTSO

MTSO search for the location of the mobile phone

Mobile phone is found, the MTSO transmits a ringing

signal

When the mobile phone is answered, assigns a voice

channel to the call, allowing voice communication to

begin

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비유도 매체 (cont’d)Handoff

During a conversation, the mobile phone moves from one cell

to another

Signal may become weak

MTSO monitors the level of the signal every few seconds

MTSO seeks a new cell that can accommodate the

communication better

Handoff one performed so smoothly that most of the time they

are not observed by the users

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DigitalIntegration with Satellites and PCs

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7.3 Performance

CostSpeedAttenuationEMI(Electromagnetic Interference)Security

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Performance(cont’d)

Transmission media performanceMedium Cost Speed Attenuation EMI Security

UTP

STP

Coax

Optical fiber

Radio

Microwave

Satellite

Cellular

Low

Moderate

Moderate

High

Moderate

High

High

High

Low

Low

Low

High

Low

Moderate

Moderate

Low

High

Moderate

Moderate

Low

High

High

High

Moderate

High

High

Moderate

Low

Low-high

Variable

Variable

Low

1 - 100 Mbps

1 - 150 Mbps

1 Mbps - 1 Gbps

10 Mbps - 2 Gbps

1 - 10 Mbps

1 Mbps - 10 Gbps

1 Mbps - 10 Gbps

9.6 - 19.2 Kbps

7 장 Transmission media( 전송매체 )

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Transcript of 7 장 Transmission media( 전송매체 )